Patent Document 1 below discloses a power distribution system intended for a data center that uses a multi-cell converter circuit scheme.
Patent Document 2 below discloses bi-directional multilevel AC-DC converter arrangements.
However, Patent Documents 1 and 2 do not disclose any specific example of a structure of a multi-cell converter.
In Non Patent Document 1 below, a DC power supply is realized that uses a multi-cell converter approach with series connection at an AC input and parallel connection at a DC output.
FIGS. 1A to 1C are diagrams that explain an example of a configuration of a DC power supply that uses a multi-cell converter approach that is disclosed in Non Patent Document 1 below.
FIGS. 1A to 1C illustrate an example in which implementation on a printed circuit board is performed for each converter cell (a structure of a pair of an AC/DC converter circuit and an insulated DC/DC converter circuit: 1:1), and as illustrated in FIG. 1A, the DC power supply is configured by connecting a plurality of converter cells in series at an AC input and in parallel at a DC output.
FIG. 1B illustrates an example of a circuit configuration of an AC/DC converter portion inside the converter cell of FIG. 1A, wherein an input AC is rectified through four semiconductor switching elements so as to be converted into a direct current. The direct current obtained by the conversion is held in a DC intermediate capacitor. This configuration itself is well-known to a person skilled in the art, so a further description of it is omitted.
FIG. 1C illustrates an example of a circuit configuration of a DC/DC converter portion inside the converter cell of FIG. 1A, wherein a switching control is performed by a controller (not illustrated) on four semiconductor switching elements so as to convert the DC input from the DC intermediate capacitor into AC, a primary side is connected to a secondary side in a state in which insulation has been obtained by a high-frequency transformer between the primary side and the secondary side, and a switching control is performed by a controller (not illustrated) on four semiconductor switching elements provided on the secondary side so as to convert the AC into DC to be taken out as an output.
This configuration itself is well-known to a person skilled in the art, so a further description of it is omitted.
FIG. 2 is a diagram that explains an example of a conventional structure of a printed circuit board that is disclosed in Non Patent Document 1 below. FIG. 2 illustrates a specific example in which implementation on a printed circuit board (a control board and a power board) is performed for each converter cell (an AC/DC converter circuit and an insulated DC/DC converter circuit).
As illustrated on the right side of FIG. 2, a connector (not illustrated) connects cells. This will be described in FIG. 3.
The DC power supply of Non Patent Document 1 described above is intended for a low voltage of an AC 200 V-type, but there is no mention of a voltage higher than that, that is, a high voltage such as AC 3300 V.
FIG. 3 illustrates an example of an arrangement and connection between cells when the conventional implementation on a printed circuit board is performed for each converter cell.
As illustrated in FIG. 3, each converter cell is connected to a DC output through a bus bar using a cable, and a control signal is obtained from a controller that is connected to one of the converter cells using a cable including a connector, wherein the converter cells are series connected using cables including connectors.
Further, on the primary side, converter cells are at a high potential and have potentials different from one another, so they are spaced at a predetermined insulating distance from one another.
The following problems have occurred because the structure of a printed circuit board in the example described above has a configuration as illustrated in FIGS. 2 and 3.
A connector connection or a cable connection has to be used in order to connect a DC output on the secondary side to, for example, a bus bar and in order to transmit a control signal from the controller to the converter cells, and a separate interface is needed for the connection.
Further, some measures have to be taken in advance in order not to lower the reliability due to the occurrence of a bad connector connection or a cable disconnection, which results in high costs. In addition, there is a need to provide an insulating distance between cells, so a device is made larger.    Patent Document 1: WO2014/026840A2 (FIG. 2)    Patent Document 2: EP2290799A1 (FIG. 1A)    Non Patent Document 1: Matthias Kasper, “Hardware Verification of a Hyper-Efficient (98%) and Super-Compact (2.2 kW/dm3) Isolated AC/DC Telecom Power Supply Module based on Multi-Cell Converter Approach”, (APEC 2015), P 65-P 71